1. Field of the Invention
The present invention relates to a long seeking method, and more particularly, to a long seeking method for applying additional driving forces on a sled of an optical disk drive.
2. Description of the Prior Art
In the field of designing control chipsets for optical disk drives, the control of the pick-up head is a fundamental and important issue. The control for radial movement of the pick-up head include a static tracking, a short seeking, and a long seeking (long jumping). Generally speaking, the long seeking operation often includes the following methods.(1) A stepping motor or a photo interrupter is used for identifying the actual position of the pick-up head to control the pick-up head afterwards. (2) An open loop method is used for controlling the pick-up head. (3) A velocity feedback method is used for controlling the pick-up head according to a track-crossing signal transferred from the pick-up head. In the method (1), the cost is higher, because of use of the stepping motors or the photo interrupter. In the method (2), high precision is required because of the influence of a mechanical variation. However, the method (3) is widely used for long seeking control of the pick-up head because of low cost and a great resistance to mechanical variation.
Please refer to FIG. 1, which is a schematic diagram of an optical disk drive 10 according to the prior art. The optical disk drive 10 comprises a sled 12 movably installed on the optical disk drive 10, a pick-up head 14 movably installed on the sled 12 for reading data stored on a optical disk 30, a first compensator 20 for controlling movement of the pick-up head 14 relative to the sled 12, and a second compensator 22 for controlling movement of the sled 12 relative to the optical disk drive 10. The pick-up head 14 moves within a seeking region 28. The first compensator 20 and the second compensator 22 control the pick-up head 14 and the sled 12 separately by a close-loop control, and therefore the pick-up head 14 moves with a desired velocity.
However, the structure shown in FIG. 1 for separately controlling the pick-up head 14 and the sled 14 may cause the pick-up head 14 to be out of a linear region. Please refer to FIG. 2(a) to FIG. 2(c) of prior art. FIG. 2(a) is a velocity response diagram of the pick-up head 14. FIG. 2(b) is a velocity response diagram of the sled 14. FIG. 2(c) is a relative velocity diagram of the pick-up head 14 and the sled 12. As shown in FIG. 2(a), the pick-up head 14 can reach a target velocity 32 quickly because of its lightweight. As shown in FIG. 2(b), the sled 12 needs a longer time to reach the target velocity 32 because of its heavy weight. Therefore, the relative velocity between the pick-up head 14 and the sled 12 is large as shown in FIG. 2(c). The pick-up head 14 maybe move to an edge of the seeking region 28 when the relative velocity between the pick-up head 14 and the sled 12 is too large. That is, the pick-up head 14 does not stay within a linear region of the seeking region 28 but enters into a non-linear region at the edge of the seeking region 28. This leads to bad control efficiency and a serious damage to components inside the optical disk drive 10, and the track-locking operation is negatively affected after tracking.
In order to solve the serious problem mentioned above, the prior art adopts a method of increasing the gain of the second compensator 22 shown in FIG. 1 for speeding up the response velocity of the sled 12. However, increasing the gain simultaneously generates a large variation, and greatly affects the precise control of the pick-up head 14.
It is therefore a primary objective of the claimed invention to provide a long seeking method with additional driving forces on the sled of the optical disk drive for decreasing the velocity response time of the sled and decreasing the relative velocity between the sled and the pick-up head.
Briefly, the claimed invention provides a long seeking method used in an optical disk drive. The optical disk drive comprises a sled movably installed on the optical disk drive, a pick-up head movably installed on the sled for accessing data stored in a plurality of tracks of a optical disk, and a controller for applying a velocity control force to the sled to move the pick-up head from an initial track of a seeking region of the optical disk drive to a target track of the seeking region according to a velocity profile. The seeking region comprises an acceleration region and a deceleration region. The velocity profile in the acceleration region increases and the velocity profile in the deceleration region decreases according to the moving direction of the pick-up head. The long seeking method comprises identifying a position of the pick-up head within the seeking region, applying a first driving force on the sled in addition to the velocity control force when the pick-up head is within the acceleration region, where the direction of the first driving force is the same as the moving direction of the pick-up head, and applying a second driving force on the sled in addition to the velocity control force when the pick-up head is within the deceleration region, where the direction of the second driving force is opposite to the moving direction of the pick-up head.
It is an advantage of the present invention that the long seeking method can increase the stability of the long seeking process and reduce the time needed for seeking a desired track.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.